Hollow ZIF-67-derived Co@N-doped carbon nanotubes boosting the hydrogenation of phenolic compounds to alcohols

The selective hydrogenation of highly toxic phenolic compounds to generate alcohols with thermal stability,environmental friendliness,and non-toxicity is of great importance.Herein,a series of Co-based catalysts,named Co@NCNTs,were designed and constructed by direct pyrolysis of hollow ZIF-67(HZIF-67)under H_(2)/Ar atmosphere.The evolution of the catalyst surface from the shell layer assembled by ZIF-67-derived particles to the in situ-grown hollow nitrogen-doped carbon nanotubes(NCNTs)with certain length and density is achieved by adjusting the pyrolysis atmosphere and temperature.Due to the synergistic effects of in situ-formed hollow NCNTs,well-dispersed Co nanoparticles,and intact carbon matrix,the as-prepared Co@NCNTs-0.10-450 catalyst exhibits superior catalytic performance in the hydrogenation of phenolic compounds to alcohols.The turnover frequency value of Co@NCNTs-0.10-450is 3.52 h^(-1),5.9 times higher than that of Co@NCNTs-0.40-450 and 4.5 times higher than that of Co@NCNTs-0.10-550,exceeding most previously reported non-noble metal catalysts.Our findings provide new insights into the development of non-precious metal,efficient,and cost-effective metal-organic framework-derived catalysts for the hydrogenation of phenolic compounds to alcohols.

Three-Dimensional N-Doped Carbon Nanotube/Graphene Composite Aerogel Anode to Develop High-Power Microbial Fuel Cell

Optimizing the structure of electrode materials is one of the most effective strategies for designing high-power microbial fuel cells(MFCs).However,electrode materials currently suffer from a series of shortcomings that limit the output of MFCs,such as high intrinsic resistance,poor electrolyte wettability,and low microbial load capacity.Here,a three-dimensional(3D)nitrogen-doped multiwalled carbon nanotube/graphene(N-MWCNT/GA)composite aerogel is synthesized as the anode for MFCs.Comparing nitrogen-doped GA,MWCNT/GA,and N-MWCNT/GA,the macroporous hydrophilic N-MWCNT/GA electrode with an average pore size of 4.24μm enables high-density loading of the microbes and facilitates extracellular electron transfer with low intrinsic resistance.Consequently,the hydrophilic surface of N-MWCNT can generate high charge mobility,enabling a high-power output performance of the MFC.In consequence,the MFC system based on N-MWCNT/GA anode exhibits a peak power density and output voltage of 2977.8 mW m^(−2)and 0.654 V,which are 1.83 times and 16.3%higher than those obtained with MWCNT/GA,respectively.These results demonstrate that 3D N-MWCNT/GA anodes can be developed for high-power MFCs in different environments by optimizing their chemical and microstructures.

Nitrogen-doped carbon nanotube encapsulating cobalt nanoparticles towards efficient oxygen reduction for zinc–air battery

Nitrogen-doped carbon materials encapsulating 3 d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction(ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube(N–CNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of N–CNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.

Nitrogen-Doped Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

In this study, hydrothermal carbonization(HTC)was applied for surface functionalization of carbon nanotubes(CNTs) in the presence of glucose and urea. The HTC process allowed the deposition of thin nitrogen-doped carbon layers on the surface of the CNTs. By controlling the ratio of glucose to urea, nitrogen contents of up to 1.7 wt%were achieved. The nitrogen-doped carbon nanotube-supported Pd catalysts exhibited superior electrochemical activity for ethanol oxidation relative to the pristine CNTs.Importantly, a 1.5-fold increase in the specific activity was observed for the Pd/HTC-N1.67%CNTs relative to the catalyst without nitrogen doping(Pd/HTC-CNTs). Furtherexperiments indicated that the introduction of nitrogen species on the surface of the CNTs improved the Pd(0)loading and increased the binding energy.

N-doped carbon nanotubes formed in a wide range of temperature and ramping rate for fast sodium storage

Herein,nickel@nitrogen-doped carbon nanotubes(Ni@NCNTs)are prepared by a simple and reliable method with Ni-based complex as single-source precursor.Significantly,the formation of CNTs is not susceptible to the calcination temperature and ramping rate and Ni@NCNTs can be attained from 430 to 900℃in an inert atmosphere.Then they are the first time to be applied as the anode material for sodium-ion batteries.The presence of Ni nanoparticles(NPs)facilitates the solid electrolyte interface film over the anode surface and improves the capacity retention of the host material,especially at the high rates.Furthermore,Na+diffusion is reinforced after the introduction of Ni NPs.Ni@NCNTs obtained at 500℃(Ni@NCNTs-500)exhibit the best capacity retention and rate capability.Kinetics analyses demonstrate the faster electron transportation and ion diffusion than others prepared at other temperatures.The surficial capacitance storage favors the fast electrochemistry kinetics.It delivers a high specific capacity(192 mA h g^−1 at 0.5 A g^−1),excellent cycling stability(103 mA h g^−1 after 10,000 cycles at 10 A g^−1),and outstanding high-rate capability up to 20 A g^−1(118 mA h g^−1).The related full cells confirm a high energy density of 140 Wh kg^−1 at 38.16 W kg^−1 and 44.27 W h kg^−1 at 762 W kg^−1.

Pre-fixing defects in carbon framework for revealing the active sites of oxygen reduction reaction at nitrogen-doped carbon nanotubes

Nitrogen-doped carbon-based materials are promising non-platinum group metal electrocatalysts for the oxygen reduction reaction(ORR).Understanding their ORR active sites is vital for the rational design and development of nitrogen-doped carbon-based electrocatalysts with enhanced catalytic efficiency and selectivity.However,the conclusive analysis of the ORR mechanism of nitrogen-doped carbon-based electrocatalysts remains a grand challenge because the catalysts have a complex inhomogeneous structure.Here,we elucidate this problem using nitrogen-doped carbon nanotubes framework catalysts with fixed defect concentrations prepared by pre-thermal treatment at a low temperature.The generation of defects under high-temperature treatment was effectively suppressed to enable a simple model for ORR mechanism study.A correlation between ORR pathways and the different nitrogen species in the nitrogen-doped carbon catalysts was revealed through a combination of structural and electrochemical properties investigations.Besides,our results also demonstrate the importance of defects for ORR.We believe that the results will provide instructive guidance for designing and developing novel carbon nanomaterials for ORR.

Co encapsulated N-doped carbon nanotubes as robust catalyst for valorization of levulinic acid in aqueous media

The construction of an acid resistant catalyst for synthesis of γ-valerolactone from levulinic acid in aqueous media is an important but highly challenging goal.Herein,an efficient Co@NCNT-800(after 800℃ pyrolysis) catalyst was constructed by confining Co in N-doped carbon nano-tubes(NCNT) from low cost materials by a facile strategy.Combined with the characterization results and control experiments,the in situ formed Co and Co-Ox, but not Co-Nx, proved to be the main synergistic active sites of the catalyst.It was also found that Co species are completely isolated within the bamboo-like NCNT,which could protect the metal nanoparticles from agglomeration and leaching in the strong acid reaction system.The γ-valerolactone yield of no less than 99.9% can be obtained under a relatively mild condition,and the catalytic performance has not been significantly reduced within five cycles.Therefore,this work may pave a way for the design of robust non-noble catalyst,and has potential for the production of γ-valerolactone from biomass in large-scale industries.

Ultrafine VN nanodots induced generation of abundant cobalt single-atom active sites on nitrogen-doped carbon nanotube for efficient hydrogen evolution

Development of highly active and stable non-noble electrocatalysts with well-defined nanostructures is crucial for efficient hydrogen evolution reaction(HER). Herein, a novel three-dimensional(3D) selfsupported electrode consists of vanadium nitride(VN) nanodots and Co nanoparticles co-embedded and highly active single Co atoms anchored in N-doped carbon nanotubes supported on carbon cloth(VN-Co@CoSAs-NCNTs/CC) is fabricated via a one-step in situ nanoconfined pyrolysis strategy, which shows remarkable enhanced HER electrocatalytic activity in acidic medium. During pyrolysis, the formed VN nanodots induce the generation of atomic Co Nxsites in NCNTs, contributing to superior electrocatalytic activity. Experimental and density functional theory(DFT) calculation results reveal that the electrode has multiple accessible active sites, fast reaction kinetics, low charge/mass transfer resistances,high conductivity, as well as downshifted d-band center with a thermodynamically favorable hydrogen adsorption free energy(△G_(H·)), all of which greatly boost the HER performance. As a result, the VNCo@CoSAs-NCNTs/CC electrode displays superb catalytic performance toward HER with a low overpotential of 29 mV at 10 mA cm^(-2) in acidic medium, which could maintain for at least 60 h of stable performance. This work opens a facile avenue to explore low-cost, high performance, but inexpensive metals/nitrogen-doped carbon composite electrocatalysts for HER.

Facile synthesis of Mo2C nanoparticles on N-doped carbon nanotubes with enhanced electrocatalytic activity for hydrogen evolution and oxygen reduction reactions

Developing low-cost and highly-efficient electrocatalysts for renewable energy conversion technologies has attracted even-increasing attention. Molybdenum carbide materials have recently emerged as a type of promising catalysts for electrocatalytic reactions due to the earth-abundance and Pt-resembled electrical properties. In this work, taking the advantage of the interaction between the basic groups of the Mo(VI)-melamine polymer and the acidic groups on the surface of the oxidized carbon nanotubes(CNTs), N-doped CNTs supported Mo2C nanoparticles(Mo2C/NCNT) are prepared, which exhibit outstanding electrocatalytic activity and durability for both the hydrogen evolution and oxygen reduction reactions. The impressive performance of Mo2C/NCNT can be attributed to the small size of Mo2C particles, the large exposure ratio of surface sites and the presence of N-doped CNTs. This work enlarges the multi-field applications of molybdenum carbide-base materials as promising non-precious metal electrocatalysts, which is of great significance for sustainable energy-related technologies.

Continuous nitrogen-doped carbon nanotube matrix for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Developing robust oxygen electrocatalyst with high-performance is very significant for practical rechargeable Zn-air battery.We report herein the preparation of three-dimensional continuous nanocarbon network composed of interconnected nitrogen-doped carbon nanotubes and its application as oxygen electrocatalysis in rechargeable Zn-air battery.Except the excellent electrochemical bifunctionality,this carbon nanotube matrix also delivers an impressive battery performance.Specifically,an opencircuit voltage of 1.50 V as well as a high power density of 220 m W cm^(-2) with remarkable cycling stability for 1600 h is achieved in the rechargeable Zn-air battery.The study not only provides an efficient bifunctional oxygen electrocatalyst but more importantly may pave significant concepts in designing robust electrode for long-life rechargeable Zn-air battery and other energy technologies.

Direct growth of ordered N-doped carbon nanotube arrays on carbon fiber cloth as a free-standing and binder-free air electrode for flexible quasi-solid-state rechargeable Zn-Air batteries

The development of an air electrode that is flexible in physical property and highly active and durable at different geometric status for both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is of crucial importance for the rational design of flexible rechargeable Zn-air batteries(ZABs).Considering their good elasticity,high conductivity,and superior thermal and chemical stability,carbon nanotubes have been widely used as a catalyst support in various electrocatalysts,while oxide or metal nanoparticles have been frequently deposited on the carbon nanotube substrate to perform as the active materials.Considering the poor contact between active materials and carbon nanotubes may introduce a challenge for long-term operating stability,in particular in flexible devices,pure carbon electrocatalyst is highly appreciated.Herein,a free-standing air electrode with cobalt nanoparticles encapsulated N-codoped carbon nanotube arrays uniformly grown on the surface of carbon fiber cloth is developed by a two-step in situ growth method.Such a carbon-based electrode shows outstanding activity for both ORR and OER.The flexible ZAB with such air electrode shows superior flexibility and stability working under extreme bending conditions.Moreover,the polarization and round-trip efficiency for the flexible battery is 0.67 V and 64.4%at 2 mA/cm2,respectively,even after being operated for 30 hours.This study provides a feasible way to design all carbon-based free-standing and flexible electrode and enlightens the electrode design for flexible energy conversion/storage devices.

Nickel nanoparticles supported on nitrogen-doped carbon nanotubes are a highly active,selective and stable CO_(2) methanation catalyst

CO_(2) methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route.Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation,calcination and reduction and characterized by elemental analysis,X-ray powder diffraction,H_(2) temperature-programmed reduction,CO pulse chemisorption and transmission electron microscopy.The Ni/NCNT catalysts were highly active in CO_(2) methanation at atmospheric pressure,reaching over 50% CO_(2) conversion and over 95% CH_(4) selectivity at 340℃ and a GHSV of50,000 mL g^(-1) h^(-1) under kinetically controlled conditions.The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs.The optimum loading of 30 wt%-40 wt% Ni was found to result in the highest Ni surface area,the highest degree of conversion and the highest selectivity to methane.A constant TOF of 0.3 s^(-1) was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt%to 50 wt% Ni loading.Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream.

Co-and N-doped carbon nanotubes with hierarchical pores derived from metal-organic nanotubes for oxygen reduction reaction

Biomolecules with a broad range of structure and heteroatom-containing groups offer a great opportunity for rational design of promising electrocatalysts via versatile chemistry.In this study,uniform folic acid-Co nanotubes(FA-Co NTs) were hydrothermally prepared as sacrificial templates for highly porous Co and N co-doped carbon nanotubes(Co-N/CNTs) with well-controlled size and morphology.The formation mechanism of FA-Co NTs was investigated and FA-Co-hydrazine coordination interaction together with the H-bond interaction between FA molecules was characterized to be the driving force for growth of one-dimensional nanotubes.Such distinct metal-ligand interaction afforded the resultant CNTs rich Co-N_x sites,hierarchically porous structure and Co nanoparticle-embedded conductive network,thus an overall good electrocatalytic activity for oxygen reduction.Electrochemical tests showed that Co-N/CNTs-900 promoted an efficient 4 e ORR process with an onset potential of 0.908 V vs.RHE,a limiting current density of 5.66 mA cm^(-2) at 0.6 V and a H_2 O_2 yield lower than 5%,comparable to that of 20%Pt/C catalyst.Moreover,the catalyst revealed very high stability upon continuous operation and remarkable tolerance to methanol.

Cobalt phosphide nanoparticles supported within network of N-doped carbon nanotubes as a multifunctional and scalable electrocatalyst for water splitting

In order to realize industrial production of hydrogen through water splitting,it is essential to develop a cost-efficient and scalable approach to synthesize nonprecious electrocatalysts with sufficiently high activity and stability to replace commercial noble-metal-based electrocatalysts.Herein we synthesize cobalt phosphide nanoparticles dispersed within nitrogen-doped carbon nanotube network(CP@NCNT) via scalable spray drying and thermal treatments.As a multifunctional electrocatalyst,the CP@NCNT hybrid delivers outstanding activity for HER(in both acidic and alkaline electrolytes),OER and overall water splitting.Remarkably,it shows an ultra-low overpotental of 94 mV to obtain 10 mA cm-2 in HER.It also demonstrates outstanding activity in overall water splitting,requiring only 1.619 V to deliver 10 mA cm-2with more than 72 h’ long-term stability.The combination of notable performance,multi-functionality and highly scalable spray-drying synthesis method enables this material as a novel and cost-efficient transition metal-based electrocatalysts for overall water splitting.

Enhanced Electrochemical Capacitance of Nitrogen-Doped Carbon Nanotubes Synthesized from Amine Flames

This paper presents a new process for synthesizing a kind of nitrogen- doped carbon nanotubes (N-CNTs) with primarily a ‘graphite-like’ structure at N substitutions from flames using n-propylamine and n-butylamine as fuels. When the N-CNTs are used as the supercapacitor electrode materials, they exhibit a much larger capacitance than the regular carbon nanotubes (CNTs). It is proposed that the high proportional ‘graphite-like’ N dopant in the as-grown N-CNTs improves their surface chemical activity and conductivity and then results in a desirable performance for electro-chemical capacitors.

Effects of Potassium and Manganese Promoters on Nitrogen-Doped Carbon Nanotube-Supported Iron Catalysts for CO_2 Hydrogenation

氮掺杂碳纳米管(NCNTs)作为载体负载铁(Fe)纳米颗粒,可应用于CO_2多相催化加氢反应(633 K和25 bar)。当将钾(K)和锰(Mn)作为助催化剂时,Fe/NCNT展现出优异的CO_2加氢性能,在体积空速(GHSV)为3.1 L·g^(–1)·h^(–1)时转化率可达34.9%。当使用K作为助催化剂时,反应对烯烃和短链烷烃具有高的选择性。当K和Mn同时作为助催化剂时,其催化活性能够稳定地维持60 h。助催化剂Mn的结构效应通过X射线衍射、氢气程序升温还原以及近边X射线吸收精细结构进行表征。助催化剂Mn不仅能够稳定中间态FeO,且能降低程序升温还原的起始温度。通过探针反应NH3的催化分解来表征助催化剂效应。当K和Mn作为助催化剂时,Fe/NCNT具有最好的催化活性。在还原条件下,当K作为助催化剂时,Fe/NCNT具有最优异的热稳定性。

A reevaluation of the correlation between the synthesis parameters and structure and properties of nitrogen-doped carbon nanotubes

Nitrogen-doped carbon nanotubes（NCNTs） were synthesized by chemical vapor deposition using cobaltbased oxides as catalyst and ethylenediamine（EDA） as carbon/nitrogen precursor. The influence of growth time,EDA concentration and growth temperature on the morphology,yield,composition,graphitization and oxidation resistance of the NCNTs was systematically investigated by using Raman spectroscopy,temperature-programmed oxidation and other techniques. The NCNT growth from ethylenediamine with a high N/C ratio involves several processes including mainly（1） catalytic growth of NCNTs,（2） homogeneous gas-phase decomposition of EDA,（3） non-catalytic deposition of pyrolytic carbon/nitrogen species and（4）surface etching of amorphous carbon or carbon at defect sites through gasification. At a later growth stage the etching process appears to be dominating,leading to the thinning of nanotubes and the decrease of yield.Moreover,the surface etching through carbon gasification strongly influences the structure and degree of graphitization of NCNTs.

Facile Fabrication of Platinum Nanoparticles Supported on Nitrogen-doped Carbon Nanotubes and Their Catalytic Activity

在温和状况下面的一个灵巧的受精方法在做氮的碳 nanotubes (CN x ) 上与 47 nm 的一种狭窄的尺寸为高度驱散的磅 nanoparticles 的合成被设计。CN x 不需要任何东西预先出现修正由于固有的化学活动。Pt/CN x 的结构和自然被 X 光检查衍射描绘，扫描电子显微镜学，传播电子显微镜学和精力散光谱学光谱。所有试验性的结果表明在 CN x 的大量做的氮原子为捕获磅(IV ) 是几乎有效的离子。改进表面氮功能和 hydrophilicity 在 CN x 表面上贡献了磅 nanoparticles 的好分散和固定。Pt/CN x 在 allyl 酒精的加氢用作活跃、可重用的催化剂。这能被归因于在磅和支持之间的磅 nanoparticles 和更强壮的相互作用的高分散，它阻止了磅 nanoparticles 聚集进不太活跃的磅黑色并且从也沥滤。

MoP nanoparticles encapsulated in N-doped carbon nanotubes as sulfur host for advanced lithium-sulfur batteries

The low electrical conductivity of sulfur,strong volume expansion,shuttle effect,and sluggish redox reactions in Li-S batteries limit their practical application.MoP nanoparticles encapsulated in nitrogen-doped carbon nanotubes(MoP/NC NTs)were synthesized using MoO_(3) nanorods as templates via a polypyrrole coating,heat-carbonization,MoO_(3) partial reduction,ammonia washing,and phosphorization.The MoP/NC NTs had a hollow nanostructure with a high specific surface area,which can alleviate the volume expansion of the cathode and the shuttle effect of polysulfides.The encapsulated MoP nanoparticles can anchor the polysulfides and enhance the redox reaction kinetics.Thus,the MoP/NC NTs combined with sulfur(MoP/S/NC NTs)exhibited 440.8 mAh·g^(-1) over 500 cycles at 1.0 A·g^(-1) with a decay rate of 0.06%per cycle.The density functional theory calculations and X-ray photoelectron spectroscopy results confirmed that MoP/NC NTs could anchor polysulfides and alleviate the shuttle effect by chemical interactions.This study supplies a novel route to prepare nanoparticle-embedded in N-doped carbon nanotubes for advanced Li-S battery.

Lightweight foam-like nitrogen-doped carbon nanotube complex achieving highly efficient electromagnetic wave absorption

With the increased electromagnetic wave(EMW)threat to military and human health,the develop-ment of EMW-absorbing materials is crucial.Metal-organic framework derivatives containing magnetic nanoparticles and a carbon matrix are potential candidates for designing efficient EMW-absorbing mate-rials.Herein,a zeolitic imidazolate framework-67(ZIF-67)-embedded three-dimensional melamine foam is pyrolyzed to afford carbon foam-based nitrogen-doped carbon nanotube composites,named 3D foam-like CoO/Co/N-CNTs.Magnetic CoO/Co particles are confined in the dielectric carbon nanotube skeleton.The carbon nanotubes provide considerable conductive loss,while CoO/Co magnetic particles are con-ducive to providing magnetic loss and adjusting impedance matching.Moreover,the numerous defect structures introduced by heteroatomic doping(nitrogen)cause dipole polarization and simultaneously adjust impedance matching.Meanwhile,the unique porous nanotube structure promotes multiple re-flections and scattering of EMWs,further optimizing impedance matching.CoO/Co/N-CNTs composites exhibit a minimum reflection loss of−52.3 dB at a matching thickness of 2.0 mm,while the correspond-ing effective absorption bandwidth is 5.28 GHz at a matching thickness of 2.2 mm.This study reports a novel approach to fabricating a lightweight high-performance EMW-absorbing material.